An agitated Rick Santorum on Sunday called Mitt Romney "the worst Republican in the country to put up against Barack Obama" even as it appears the former Massachusetts governor is on pace to clinch the party's nomination in June.

Santorum later lashed out at reporters, using a profane word as he accused them of "distorting" his speech.

Santorum told voters that Romney is "uniquely disqualified" to be the GOP's presidential pick and urged his supporters to stand with him even as he faces an increasingly improbable pathway to the nomination. Santorum said "the race isn't over until the people of Wisconsin sing," and urged them to give his underfunded, underdog campaign a chance to derail Romney.

"Pick any other Republican in the country. He is the worst Republican in the country to put up against Barack Obama," Santorum said at an evening rally near Racine.